This invention relates to magnetic storage apparatus capable of both high-density recording and high-speed transfer of data at a time, and particularly to one in which a high areal recording density can be achieved by suppressing the attenuation of the magnetic field intensity at high recording frequencies.
The induction-type thin-film magnetic head mounted on the conventional magnetic disk apparatus has its magnetic poles made of a NiFe alloy thin film of about 3 xcexcm in thickness. Since the resistivity of this NiFe alloy film is as low as around 16 xcexcxcexa9-cm, the eddy-current loss is increased at high frequencies so that the recording magnetic field intensity is reduced. The amount of writing blur or overwrite value is changed with the recording frequency under the influence of this eddy-current loss. As a conventional example, there is, for example, JP-A-58-115612, in which it is described that the generation of eddy current affects the low-resistivity permalloy (such as a NiFe alloy) in such a way as to reduce its high-frequency permeability, and thus, good reproduction characteristics (sensitivity) are not obtained. Because of these problems, the recording frequency at which the NiFe alloy thin-film head can operate is limited to about 30 MHz. On the other hand, the storage capacity of the magnetic disk apparatus has been steadily increased year after year, up to the extent that the now available 3.5-inch disk storage apparatus has an areal recording density of 350 Mb/in2, maximum. The data recording frequency at which this apparatus can record is around 27 MHz, which is near the limit of the induction-type thin-film magnetic head using NiFe alloy thin films.
It is an object of the invention to provide a magnetic storage apparatus using magnetic heads for high-speed access and high-speed transfer without changing the writing blur or overwrite value as the recording frequency changes. The above object can be achieved by designing the thickness, resistivity and relative permeability considering the eddy current loss in the magnetic pole film of the recording head so as to prevent the writing blur or overwrite value from varying as the recording frequency changes, and by selecting the data recording frequency to be high, and by rotating the magnetic disk fast.
In other words, according to the first invention, there are provided:
(1) a magnetic storage apparatus having means for achieving a media data rate of 15 megabytes per sec. or above and an areal data-recording density of 500 megabits per square inch or above;
(2) a magnetic storage apparatus according to item (1), wherein when information is recorded on a magnetic disk of 3.5-inch diameter or below, this disk is rotated at a rate of 4000 rpm or above in the recording/reproduction mode and the recording frequency is selected to be 45 MHz or above;
(3) a magnetic storage apparatus according to item (1), wherein a metal magnetic film having a coercive force of 2 kOe or above is formed on the magnetic disk used;
(4) a magnetic storage apparatus according to item (1), wherein the rise time of the recording current is selected to be 5 nanosecond (ns) or below;
(5) a magnetic storage apparatus according to item (4), wherein the recording coil 25, 25xe2x80x2 (FIGS. 4, 8) of an induction type magnetic head used for recording information on the magnetic disk medium is formed by a thin-film process and has three terminals A, B, C, the inductance between the terminals is one microhenry (xcexcH) or below;
(6) a magnetic storage apparatus according to item (5), wherein the recording coil 25, 25xe2x80x3 (FIGS. 4, 9) of the induction type magnetic head used for recording information on the magnetic disk medium has a double-layer structure in which the first layer coil 92 and the second layer coil 94 have an equal number of turns but are wound in opposite directions to each other; and
(7) a magnetic storage apparatus according to item (5) wherein the recording coil 25, 25xe2x80x2 (FIGS 4, 8) of the induction type magnetic head used for recording information on the magnetic disk medium has a single-layer structure 80 (FIG. 8) in which an intermediate-point terminal is connected at a mid point (c) between both coil ends (a), (b) which mid point corresponds to half the total number of turns of the coil, and a current (FIG. 10) flowing between the terminals (c) and (a) is opposite in phase to a current flowing between the terminals (c) and (b).
According to the second invention, there are provided:
(8) a magnetic storage apparatus having means for causing a relation of xcexcd2/xcfx81xe2x89xa6500 to be satisfied where d (xcexcm) is the thickness of a magnetic film which forms the recording magnetic poles of a magnetic head for recording data or for recording/reproduction of data, xcfx81 (xcexcxcexa9-cm) is the resistivity, and xcexc is the relative permeability in a low-frequency region;
(9) a magnetic storage apparatus according to item (8), wherein at least part of the recording magnetic poles of the magnetic head for recording data or for recording/reproduction of data has a multi-layered structure of alternate magnetic layer and insulating layer and the thickness of the multi-layered film is 2.7 xcexcm or below;
(10) a magnetic storage apparatus according to item (8), wherein at least part of the recording magnetic poles of the magnetic head for recording data or for recording/reproduction of data is made of Co-based amorphous alloy or Fe-based amorphous alloy;
(11) a magnetic storage apparatus according to item (8), wherein at least part of the recording magnetic pole material of the magnetic head for recording data or for recording/reproduction of data has an oxygen concentration distribution in a metal magnetic substance;
(12) a magnetic storage apparatus according to item (11), wherein the recording magnetic pole material of the magnetic head has oxygen-rich particles mixed of which the size is in a range between 0.5 nm and 5 nm inclusive;
(13) a magnetic storage apparatus according to item (11), wherein the oxygen-rich particles mixed in the recording magnetic pole material of the magnetic head contain at least one of the elements Zr, Y, Ti, Hf, Al and Si;
(14) a magnetic storage apparatus according to item (8), wherein the magnetomotive force of the recording head for recording data or for recording/reproduction of data, or the product of the recording current and the number of turns of coil of the head is selected to be 0.5 amperexc2x7turn (AT) or above;
(15) a magnetic storage apparatus according to item (8), wherein at least part of the recording magnetic poles of the magnetic head for recording data or for recording/reproduction of data has a resistivity of 40 xcexcxcexa9-cm or above and a relative permeability of 500 or above;
(16) a magnetic storage apparatus according to item (8), wherein at least part of the recording magnetic poles of the magnetic head for recording data or for recording/reproduction of data has a relative permeability of 500 or below and a resistivity of 40 xcexcxcexa9-cm or below;
(17) a magnetic storage apparatus according to item (8), wherein the rise time of recording current is 5 nanosecond (ns) or below.
(18) a magnetic storage apparatus according to item (17), wherein the recording coil of an induction type magnetic head for recording information on a magnetic disk medium is formed by a thin film process and has three terminals, and the inductance between the terminals is one microhenry (xcexcH) or below;
(19) a magnetic storage apparatus according to item (18), wherein the recording coil 25xe2x80x3 (FIG. 9) of the induction type magnetic head for recording information on the magnetic disk medium has a double-layer structure in which the first layer coil 92 and the second layer coil 94 have an equal number of turns but are wound in opposite directions to each other.
(20) a magnetic storage apparatus according to item (18), wherein the recording coil 25xe2x80x2 (FIG. 8) of the induction type magnetic head used to record information on the magnetic disk medium has a single-layer structure 80 in which an intermediate-point terminal is connected at a mid point (c) between both coil ends (a), (b) which mid point corresponds to half the total number of turns of the coil, and a current (FIG. 10) flowing between the terminals (c) and (a) is opposite in phase to a current flowing between the terminals (c) and (b); and
If the high-frequency loss (tan xcex4) in the magnetic film is due to only the eddy current loss, it can be expressed by                                                                         tan                ⁢                                  xe2x80x83                                ⁢                δ                            =                                                μ                  xe2x80x3                                /                                  μ                  xe2x80x2                                                                                                        =                                                R                  /                  ω                                ⁢                                  xe2x80x83                                ⁢                L                                                                                        =                                                μ                  0                                ⁢                μ                ⁢                                  xe2x80x83                                ⁢                π                ⁢                                  xe2x80x83                                ⁢                                  d                  2                                ⁢                                  f                  /                  C                                ⁢                                  xe2x80x83                                ⁢                ρ                                                                        (        1        )            
where xcexcxe2x80x2 and xcexcxe2x80x3 are the real part and imaginary part of the complex permeability, C is a constant depending on the film shape, and xcexc0 is the permeability of vacuum. By substituting the relative permeability xcexc, thickness d and resistivity xcfx81 peculiar to the magnetic film into Equation (1), it is possible to estimate the eddy current loss, tan xcex4 at a frequency f. Since it can be considered that the change of head efficiency (efficiency for conduction of magnetic flux) to frequency is proportional to the change of the real part of the complex permeability, the frequency dependency of the head efficiency can be estimated from the cosine of the xcex4 which is calculated from Equation (1). That is, the head efficiency xcex7 at each frequency can be expressed by the following equation:
xcex7=cos [arc tan (xcexc0xcexcxcfx80d2f/Cxcfx81)]xe2x80x83xe2x80x83(2)
Thus, the head efficiency xcex7 at a given frequency f can be extrapolated from the value xcexcd2/xcfx81 in Equation (2) where xcexc is the relative permeability, d is the thickness and xcfx81 is the resistivity, peculiar to the magnetic film.
If this head is combined with a magnetic disk of a metal magnetic film which has small writing blur or overwrite value variation at the time of high frequency recording and of which the coercive force is 2 kOe or above, it is possible to provide a high-performance magnetic storage apparatus capable of operating at an areal recording density of 500 Mb/in2 or above, recording frequency of 45 MHz or above and media data rate of 15 MB/s or above.
FIG. 7 shows the relation between the cost of input/output unit and the transfer speed per magnetic disk storage apparatus which constitutes the input/output unit, in which case a data bus of two-byte width Fast and Wide SCSI (Small Computer System Interface) is used for the input/output (I/O) interface. From FIG. 7, it will be seen that when the data bus of two-byte width Fast and Wide SCSI interface is used, data transfer can be made at a maximum of 20 MB/s. In this case, if the transfer speed per magnetic disk storage apparatus is 15 MB/s or above, the cost of input/output unit can be reduced.
Moreover, if the capacity per disk unit is 550 MB, it is possible to handle OS (Operation Software) such as Windows or Workplace. In order to realize this capacity by a single 3.5-inch magnetic disk, it is necessary that the areal data-recording density be selected to be 500 Mb/in2 or above.